Murphtone Hit the nail on the head and an NBC exec said as much to me two weeks ago. I live in Burbank and our kids participate in the same activity. While talking he was telling me how bad buisness is. I told him the last NBC show I watched regularly was Chuck. He told me The Network wished they had shows with Chucks numbers now, and the only show they can launch a new show after is the Voice.
To the OP I would say that no show is perfect, their are writing flaws. I'm currently watching Season ( I'm at The Leftovers) and It finally dawned on me, why didn't Moma B use the PSP intersect suppressor on Volkoff. and we could of avoided all the drama.
Chuck had a good run. It did OK and advertisers liked it because of the loyal fans. If you want to look for reasons it's over I would say look outside the production team to the network. How many Chuck promo's did you see on TV? None, NBc didn't promote it, never supported it and moved it. That and timing probably contributed to it's demise. At the end of the 5th year I'm guessing a lot of the stars contracts would be up. They would of had to pony up $$$ for Yvonne and Zach and other cast members. If the show would of survived I'm guessing Adam Baldwin would of been written out ( since he was the highest paid regular for most the series) and I don't think the show made enough money to cover the vig on new contracts.
On another note. I REALLY, REALLY, REALLY, MISS TALKING Chuck WITH ALL MY FRIENDS HERE.